This invention relates to a process for producing acetic anhydride which comprises reacting methyl acetate or dimethyl ether with carbon monoxide in the presence of a catalyst and a co-catalyst.
In the prior art, the known catalysts for producing carboxylic anhydrides from carboxylic esters or ethers and carbon monoxide include the following:
(i) a catalyst comprising a noble metal belonging to Group VIII of the Periodic Table, such as rhodium, a halide and a third component as disclosed in Japanese Patent Publication (Kokoku) No. 3926/1977; Japanese Patent Publication (Kokai) No. 65709/1976 and Japanese Patent Publication (Kokai) No. 115403/1976, and PA1 (ii) a catalyst comprising nickel or cobalt, a halide and a third component as disclosed in Japanese Patent Publication (Kokai) No. 59214/1979 assigned to the assignee of this application, U.S. Pat. Nos. 4,002,677, 4,002,678 and 2,729,651. PA1 (b) Wherein R.sup.1 is hydrogen, alkyl having 1-10 carbon atoms, cycloalkyl having 3-10 carbon atoms, or aryl and R.sup.2 and R.sup.3 are taken together and represents methylene or polymethylene having 2-5 carbon atoms; the compounds include, for example, pyrrolidine, N-methyl pyrrolidine, piperidine or N-phenyl piperidine: PA1 (c) wherein R.sup.1 and R.sup.2 may be the same or the different and independently represent hydrogen, alkyl having 1-10 carbon atoms, cycloalkyl having 3-10 carbon atoms, or aryl and having 6-10 carbon atoms and R.sup.3 is aliphatic saturated acyl, or R.sup.1 is hydrogen, alkyl having 1-10 carbon atoms, cycloalkyl having 3-10 carbon atoms or aryl having 6-10 carbon atoms, and R.sup.2 and R.sup.3 are taken together and represent lactam ring (in which R.sup.2 and R.sup.3 are bonded through carboxy polymethylene; the compounds include, for example carboxylamides such as acetamide, N, N-dimethylacetamide, acetanilide, N-methyl-N-phenylacetamide, and lactams, such as N-methyl-pyrrolidinone: PA1 (d) wherein at least one of R.sup.1, R.sup.2 and R.sup.3 is carboxy-methyl and the remainder is hydrogen, alkyl having 1-10 carbon atoms, cycloalkyl having 3-10 carbon atoms or aryl having 6-10 carbon atoms; the compounds include, for example carboxylic acid derivatives, such as N, N-dimethyl glycine, N,N-diethyl glycine, iminodiacetic acid, N-methyl iminodiacetic acid, or nitrilo-triacetic acid: PA1 (a) wherein R.sup.4, R.sup.5, R.sup.6 and R.sup.7 may be the same or different and independently hydrogen, alkyl having 1-10 carbon atoms, cycloalkyl having 3-10 carbon atoms, or aryl and R.sup.8 is methylene group or polymethylene group having 2-10 carbon atoms, phenylene, or carbonyl group M.sup.1 and M.sup.2 are N, P, Sb or As. The compounds include, for example, ethylene bis (disphenolphosphine), phenylene bis (dimethylphosphine), bis (diphenylarsino) ethane, bis (di-iso-propylarsino) hexane, bis (diethylstibino) pentane, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, N,N,N',N'-tetra-n-propylethylenediamine, N,N,N', N'-tetramethylmethylenediamine, N,N,N',N'-tetramethyl urea, N-methyl-2-pyrrodinone and triethylenediamine, PA1 (b) R.sup.4 and R.sup.6 may be the same or different and independently represent hydrogen, alkyl having 1-10 carbon atoms, cycloalkyl having 3-10 carbon atoms or aryl and R.sup.5 and R.sup.7 are taken together and represent methylene or polymethylene having 2-5 carbon atoms and R.sup.8 is methylene or polymethylene having 2-5 carbon atoms; the compounds include, for example, heterocyclic compounds, such as piperazine, N-methyl-piperazine, N-ethylpiperazine, or 2-methyl-N, N'-dimethylpiperazine. PA1 (c) other compounds include, for example, tris (diethylaminomethyl) stibine, 2,5-dicarboxy-piperazine, cyclohexane-1, 2-diamine-N,N,N',N'-tetraacetic acid or salts thereof, tetramethylester thereof, ethylene-diaminetetraacetic acid, or its salt or tetramethyl-ester thereof, 1,4-azabicyclo [2,2,2] octane, methyl substituted 1,4-diazabicyclo [2,2,2] octane, adiponitrile or N-methyl-morpholine. PA1 (i) metal of group IVB or a compound of the metal; PA1 (ii) metal of Group IVB or a compound of the metal and metal of Group IIA or a compound of the metal; PA1 (iii) metal of Group IVB or a compound of the metal and metal of Group IA or a compound of the metal; PA1 (iv) metal of Group IVB or a compound of the metal, metal of Group IA or a compound of the metal and metal of Group IIA or a compound of the metal.
However, catalyst (i) contains expensive rhodium as shown in Hydrocarbon Processing 54, June 83 (1975).
In case of producing carboxylic anhydrides from carboxylic esters or ethers and carbon monoxide by using a rhodium catalyst, a rhodium complex has to be prevented from being reduced to metallic rhodium under a reducing atmosphere as disclosed in KAKTAF, 29 (5), page 376 (1976) or the rhodium component has to be prevented from being scattered from the reaction system during the operation of separating the product as disclosed in Japanese Patent Publication (Kokai) No. 90204/1978.
In Japanese Patent Publication (Kokai) No. 59214/1979 assigned to the assignee of this invention, a nickel catalyst has been proposed in place of the noble metal catalyst. However, when using catalyst (ii) as disclosed in Japanese Patent Publication (Kokai) No. 59214/1979 and U.S. Pat. No. 2,729,651 the reaction rate is low, and the reaction conditions are severe.